1. 將json文件轉化為字串

   StringBuilder sb=null;
   try {
       //獲取檔案輸入流
       InputStream input = getAssets().open(fileName);
       //快取輸入流
       BufferedReader br=new BufferedReader(new InputStreamReader(input));
        //定義的自定義儲存資料庫
       sb = new StringBuilder();
       //臨時儲存字串
       String con;
       //迴圈獲取輸入流中的資料
       while((con=br.readLine())!=null){
           //將資料存在儲存器中
           sb.append(con);
       }
   
   } catch (IOException e) {
       // TODO Auto-generated catch block
       e.printStackTrace();
   }
   //返回儲存器中的字串
   return sb.toString();
    
   

2. 將網路請求的json流轉化為字串的工具類
   //需要傳過來一個輸入流和編碼格式

import android.os.AsyncTask;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

/**
 * 使用AsyncTask+HttpURLConnection請求資料
 * Created by e531 on 2017/10/12.
 */
public class
 
 MyTask extends AsyncTask<String,Void,String> {

    //申請一個介面類物件
    private  Icallbacks icallbacks;

    //將無參構造設定成私有的，使之在外部不能夠呼叫
    private MyTask(){}

    //定義有參構造方法
    public MyTask(Icallbacks icallbacks) {
        this.icallbacks = icallbacks;
    }

    @Override
    protected String doInBackground(String... params) {
        String str=""
 
;

        try {
             //使用HttpUrlConnection
            URL url=new URL(params[0]);
            HttpURLConnection connection=(HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setReadTimeout(5000);
            connection.setConnectTimeout(5000);

            if(connection.getResponseCode()==200){
                InputStream inputStream=connection.getInputStream();
                //呼叫工具類中的靜態方法
                str=StreamToString.streamToStr(inputStream,"utf-8");
            }

        } catch (MalformedURLException e) {
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }


        return str;
    }

    @Override
    protected void onPostExecute(String s) {
        super.onPostExecute(s);
        //解析，封裝到bean,更新ui元件
        icallbacks.updateUiByjson(s);



    }
    //定義一個介面
    public interface Icallbacks{
        /**
         * 根據回傳的json字串，解析並更新頁面元件
         * @param jsonstr
         */
        void updateUiByjson(String jsonstr);
    }
}

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;

/**
 * Created by e531 on 2017/10/12.
 */
public class StreamToString {

    public static String streamToStr(InputStream inputStream,String chartSet){

        StringBuilder builder=new StringBuilder();
        try {
            BufferedReader br=new BufferedReader(new InputStreamReader(inputStream,chartSet));
            String con;
            while ((con=br.readLine())!=null){
                builder.append(con);
            }

            br.close();
            return builder.toString();


        } catch (Exception e) {
            e.printStackTrace();
        }


        return "";
    }
}